#include <stdio.h>

int main()
{
    int n = 0;
    scanf("%d", &n);
    if(n == 0)
    {
        printf("整数之和为%d", n);
        return 0;
    }
    int sum = (1 + n) * n / 2;
    printf("整数之和为%d", sum);
    return 0;
}